1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method for the same, and more particularly, to an image sensor and a method for manufacturing the image sensor.
2. Discussion of the Related Art
An image sensor denotes a semiconductor device that converts an optical image into an electrical signal.
A charge coupled device (CCD), one type of image sensor, has metal oxide silicon (MOS) capacitors disposed very close to one another, wherein charge carriers are stored in and transferred from the capacitors.
A complementary MOS (CMOS) image sensor employs a switching method which uses a CMOS technology to form MOS transistors corresponding to the number of pixels, and successively detects outputs using the MOS transistors. The CMOS technology uses a control circuit and a signal processing circuit as peripheral circuits.
In the CMOS image sensor, for example, incident light reaches a photodiode (not shown) by passing through a micro lens (not shown) and a color filter (not shown), accordingly generating electrons and holes in a silicon substrate by conversion from optical energy. Thus-generated electrons are converted to and read out as voltage signals, which are processed and converted back to the form of images.
As the device size is reduced, the pixel size and a light receiving area are accordingly reduced. Consequently, the sensitivity may deteriorate. To this end, a 3D image sensor has recently been developed, wherein the light receiving area is formed in an upper part of a passivation region.
Hereinafter, the structure of a back-side illumination (BSI) image sensor of the 3D image sensors will be briefly described with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing a 3D image sensor according to one related art.
The image sensor 10 includes a passivation layer 30, interlayer dielectrics 32, 34 and 36, a gate electrode 40, contacts 50, metal layers 52, a super via 60, color filters 80 and a metal pad 90.
Referring to FIG. 1, after an image sensor wafer 22 is completely constructed, the wafer 22 is turned upside down and bonded to another wafer 20.
In the bonded state, Chemical Mechanical Polishing (CMP) or backgrinding is performed with respect to a backside of the wafer 22, so that a silicon light receiving part 70 has a thickness of several micrometers (μm).
Through the light receiving part 70, data can be read out from the pixels to the super via 60.
However, according to the above-described image sensor, the metal pad 90 at the upper part of the super via 60 is formed directly on the silicon substrate 70. In this case, a short circuit may occur between the metal pad 90 formed of aluminum (Al) and the light receiving part 70 formed of Si.
FIG. 2 shows an example of the connection structure between a super via and a metal pad of a 3D image sensor according to another related art.
Referring to FIG. 2, plugs 62 protrude upward out of light receiving parts 72, to prevent the electric short circuit occurring in the BSI image sensor shown in FIG. 1.
Next, an insulating layer 100 is vapor-deposited on an upper part of the light receiving part 72 and the protruding plugs 62. Upper surfaces of the plugs 62 are exposed by performing CMP on an upper part of the insulating layer 100. Next, metal pads 92 are formed on the exposed upper surfaces of the plugs 62 and the upper part of the insulating layer 100. The light receiving part 72, the super via 62 and the metal pad 92 shown in FIG. 2 have the same functions as the light receiving part 70, the super via 60 and the metal pad 90 of FIG. 1, respectively.
However, the image sensor introduced in FIG. 2 has a risk in that the wafer 22 may be broken during the CMP process performed on the insulating layer 100.